mcp-js (V8 sandbox)

為什麼要用

核心特性

Isolated V8 runtime, no Node syscalls by default
Persistent heap snapshots (local FS or S3)
Multiple named contexts per session
Built in Rust — fast startup, low memory overhead
Predictable timeouts and memory caps

即時演示

實際使用效果

mcp-js-v8.replay ▶ 就緒

0/0

安裝

選擇你的客戶端

~/Library/Application Support/Claude/claude_desktop_config.json · Windows: %APPDATA%\Claude\claude_desktop_config.json

{
  "mcpServers": {
    "mcp-js-v8": {
      "command": "mcp-js",
      "args": []
    }
  }
}

開啟 Claude Desktop → Settings → Developer → Edit Config。儲存後重啟應用。

~/.cursor/mcp.json · .cursor/mcp.json

{
  "mcpServers": {
    "mcp-js-v8": {
      "command": "mcp-js",
      "args": []
    }
  }
}

Cursor 使用與 Claude Desktop 相同的 mcpServers 格式。專案級設定優先於全域。

VS Code → Cline → MCP Servers → Edit

{
  "mcpServers": {
    "mcp-js-v8": {
      "command": "mcp-js",
      "args": []
    }
  }
}

點擊 Cline 側欄中的 MCP Servers 圖示，然後選 "Edit Configuration"。

~/.codeium/windsurf/mcp_config.json

{
  "mcpServers": {
    "mcp-js-v8": {
      "command": "mcp-js",
      "args": []
    }
  }
}

格式與 Claude Desktop 相同。重啟 Windsurf 生效。

~/.continue/config.json

{
  "mcpServers": [
    {
      "name": "mcp-js-v8",
      "command": "mcp-js",
      "args": []
    }
  ]
}

Continue 使用伺服器物件陣列，而非映射。

~/.config/zed/settings.json

{
  "context_servers": {
    "mcp-js-v8": {
      "command": {
        "path": "mcp-js",
        "args": []
      }
    }
  }
}

加入 context_servers。Zed 儲存後熱重載。

claude mcp add mcp-js-v8 -- mcp-js

一行命令搞定。用 claude mcp list 驗證，claude mcp remove 移除。

使用場景

實戰用法： mcp-js (V8 sandbox)

Iteratively shape a JSON dataset across multiple tool calls

👤 Data wranglers ⏱ ~15 min intermediate

何時使用： Multi-step transform where you want to keep intermediate variables.

前置條件

Server/skill installed and authenticated — See repo README

步驟

Load data

eval_js: const data = await fetch('https://example.com/data.json').then(r => r.json()); data.length✓ 已複製

→ Length printed
Iterate

eval_js: const filtered = data.filter(x => x.status === 'active'); filtered.length✓ 已複製

→ Filtered count — data still in heap
Snapshot

snapshot_save name=cleanup-2026-05-21✓ 已複製

→ Saved

結果： Notebook-style JS sessions without a notebook.

注意事項

V8 isolate has no Node APIs by default. If you need fs/net, opt in explicitly — V8 isolate has no Node APIs by default. If you need fs/net, opt in explicitly — and remember Claude can then write to disk.

搭配使用： filesystem

組合

與其他 MCP 搭配，撬動十倍槓桿

mcp-js-v8 + filesystem

Pair with filesystem for complementary capabilities

Use this server together with filesystem to complete a multi-step task.✓ 已複製

工具

此 MCP 暴露的能力

工具	輸入參數	何時呼叫	成本
eval_js	context_id, code	Run a JS snippet, optionally with state from prior calls	free (local)
snapshot_save	context_id, name	Persist current heap	free / S3 PUT
snapshot_load	name	Resume an earlier session	free / S3 GET

成本與限制

運行它的成本

API 配額: See provider docs for rate limits
每次呼叫 Token 數: Varies by tool
費用: See repo README for pricing details
提示: Cache tool results and avoid repeated identical calls.

安全

權限、密鑰、影響範圍

憑證儲存： Use environment variables; never commit secrets

資料出站： Tool calls go to the provider's API as documented

故障排查

常見錯誤與修復

context expired

Contexts expire after the configured idle window. Use snapshot_save before long pauses.

驗證： Reload from snapshot_load

memory limit exceeded

Raise MCP_JS_MAX_HEAP_MB or chunk the input.

驗證： Reduce dataset size and retry

替代方案

mcp-js (V8 sandbox) 對比其他方案

替代方案	何時用它替代	權衡
yepcode/mcp-server-js	You want hosted execution with secrets	Hosted/paid vs local/free